1. Field of the Invention
The present invention relates to a collecting unit used for a semiconductor processing apparatus for processing a target substrate, such as a semiconductor wafer, and a film formation apparatus for a semiconductor process provided with the collecting unit. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an FPD (Flat Panel Display), e.g., an LCD (Liquid Crystal Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices for constituting semiconductor integrated circuits, a target substrate, such as a semiconductor wafer (made of, e.g., silicon) is subjected to various processes, such as film formation, etching, oxidation, diffusion, reformation, annealing, and natural oxide film removal. There is a vertical film formation apparatus (of the so-called batch type), which performs a film formation process on a plurality of semiconductor wafers all together.
In the vertical film formation apparatus, semiconductor wafers are first transferred from a wafer cassette onto a vertical wafer boat and supported thereon at intervals in the vertical direction. The wafer cassette can store, e.g., 25 wafers, while the wafer boat can support 30 to 150 wafers. Then, the wafer boat is loaded into a process container of the hot wall type from below, and the process container is airtightly closed. Then, a predetermined film formation process is performed, while the process conditions, such as process gas flow rates, process pressures, and process temperatures, are controlled.
Reaction products generated during the film formation process are deposited (adhered) not only on the surface of the semiconductor wafer, but also on, e.g., the inner surface of the process container and other members, the latter being as by-product films. If the film formation process is continued while by-product films are present on the inner surface of the process container, a stress is generated and causes peeling of some of the by-product films and the quartz of the process container due to a difference in coefficient of thermal expansion between the quartz and by-product films. Consequently, particles are generated, and may decrease the yield of semiconductor devices to be fabricated and/or deteriorate some components of the processing apparatus.
In order to solve this problem, cleaning of the interior of the process container is performed after the film formation process is repeated several times. Conventionally, for example, hydrogen fluoride (HF) solution is typically used to clean the process container. In this case, by-product films are removed by wet etching. However, this wet etching requires work operations for detaching the process container, manually cleaning the container, and then reattaching and adjusting the container. Further, the heat-processing apparatus needs to be shut down for a long time, thereby increasing downtime of the apparatus and lowering the operating rate thereof.
In light of this problem, in recent years, dry cleaning accompanied by no disassembling of a process container is widely used. In this dry cleaning, the interior of the process container is heated at a predetermined temperature by a heater, and a cleaning gas, such as a mixture gas of fluorine and a halogen-containing acidic gas, is supplied into the reaction tube. The by-product films deposited on the inner surface of the process container are thereby dry-etched and removed by the cleaning gas. This trend in the cleaning process is seen not only for film formation apparatuses of the batch type but also for film formation apparatuses of the single-substrate type which process semiconductor wafers one by one.
Jpn. Pat. Appln. KOKAI Publications No. 3-31479, No. 4-155827, No. 6-151396, and No. 2004-343095 disclose techniques concerning a cleaning process of this kind.
In the film formation apparatus described above, gas exhausted from the process container contains by-products generated by film formation. Accordingly, in order to collect and remove the by-products from the exhaust gas, the exhaust system connected to the process container is provided with a collecting unit for removing the by-products.
FIG. 11 is a sectional view showing a conventional collecting unit used in a case where an SiO2 thin film is deposited by use of, e.g., TEOS (tetraethylorthosilicate) as a film formation gas. As shown in FIG. 11, the collecting unit 2 includes a cylindrical casing 4 and a trap body 6 disposed therein. The casing 4 has a gas inlet 4A formed at one end, and a lid 10 detachably connected to the other end by bolts 8. The lid 10 has a gas outlet 4B formed at the center.
The trap body 6 includes a plurality of metal fins 12, each of which is formed of a circular ring, are attached to support rods 14 at predetermined intervals. The trap body 6 includes a semispherical cover 16 on the upstream side, while the trap body 6 is attached to and supported by the lid 10 on the downstream side.
In the structure described above, during film formation, gas exhausted from a process container enters the casing 4 of the collecting unit 2 through the gas inlet 4A. This exhaust gas comes into contact with the surface of the fins 12, flows through the center of the ring fins 12, and is exhausted through the gas outlet 4B. At this time, by-products contained in the exhaust gas are deposited and trapped on the surface of the fins 12, and thereby removed from the exhaust gas.
In this case, the by-products are trapped mainly by the fins 12, but they can be deposited on any portion which the exhaust gas comes into contact with. Accordingly, the by-products are removed from the exhaust gas while some of them are deposited on the surface of the cover 16, the inner surface of the casing 4, and so forth.
The by-products thus trapped are removed along with by-products inside the process container by a cleaning gas, such as ClF3 gas or HF gas, when the cleaning gas is supplied to clean the interior of the process container. Hence, the collecting unit 2 is prevented from being clogged.